CVD deposition method to improve adhesion of F-containing dielectric metal lines for VLSI application

ABSTRACT

The present invention provides a method of depositing an amorphous fluorocarbon film using a high bias power applied to the substrate on which the material is deposited. The invention contemplates flowing a carbon precursor at rate and at a power level so that equal same molar ratios of a carbon source is available to bind the fragmented fluorine in the film thereby improving film quality while also enabling improved gap fill performance. The invention further provides for improved adhesion of the amorphous fluorocarbon film to metal surfaces by first depositing a metal or TiN adhesion layer on the metal surfaces and then stuffing the surface of the deposited adhesion layer with nitrogen. Adhesion is further improved by coating the chamber walls with silicon nitride or silicon oxynitride.

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

The present invention relates generally to the deposition of anamorphous fluorocarbon film using a high density plasma chemical vapordeposition (HDP-CVD) technique. More particularly, the present inventionrelates to a method of depositing an amorphous fluorocarbon film using ahigh bias power to enhance gap fill performance. Still further, theinvention relates to improving adhesion of a fluorine containingdielectric material to metal surfaces formed on a substrate.

BACKGROUND OF THE INVENTION

Consistent and fairly predictable improvement in integrated circuitdesign and fabrication has been observed in the last decade. However,for newer ultra large scale integration (ULSI) products with operationfrequencies approaching 1 GHz and interconnect feature sizes decreasingto ≦0.25 μm, interconnect resistance-capacitance (RC) delay willrepresent a large portion of the clock time of integrated circuits, andsignificantly new and different manufacturing approaches will berequired to achieve the required performance goals. Since RC delay isdirectly related to the interconnect resistance and dielectriccapacitance, the industry focus is on developing new materials withsignificantly lower dielectric constants and lower resistivities.

In the area of dielectrics, a great variety of materials are beinginvestigated as potential replacements for the current standard silicondioxide (SiO₂). If SiO₂, which has a dielectric constant (K)˜4, isreplaced by another material with a K value of ˜2.5, RC delay and crosstalk will be significantly reduced and overall circuit performance willbe greatly improved. It is well accepted that a dielectric constant of<3.0 will be required at the 0.18 μm device generation in order to meetexpected performance requirements.

A great variety of materials with low dielectric constants are beinginvestigated as potential candidates to replace SiO₂. However, it isimportant to remember that dielectric constant is but one of thecritical requirements that must be met. Ease of integration intoexisting and future process fabrication flows and economic factors(e.g., cost of ownership) will together decide the viability of amaterial for use as the next generation intermetal dielectric (IMD).Integration capability will be determined by critical properties such asadhesion, thermal stability, thermal conductivity, mechanical strengthand gap fill performance. Cost of ownership will be determined by costof the raw materials, cost of processing waste material (which has beenfound to be especially high with spin-on techniques), the number ofrequired integration steps as well as the capital cost of the processingequipment. The ideal low dielectric constant material will easilyintegrate into existing process flows, will use existing equipment, andcost no more than processes in use today.

CVD-deposited materials are the most promising approach for lowdielectric constant materials. It is well accepted that the mechanismsin plasma assisted depositions will lead to materials with significantlyhigher density and mechanical strength than other types of depositiontechniques. In addition, integration of a CVD film is well characterizedand fairly simple as compared with wet processes such as spin-onmethods. The potential of using existing plasma enhanced CVD equipmentand simple manufacturing methodology makes CVD materials attractive fromboth an integration and an economic standpoint.

Among the CVD-deposited materials, amorphous fluorocarbon (α-FC) ispromising for its relatively high thermal stability, low dielectricconstant value (as low as 2.3), thermal conductivity close to that ofSiO₂, and good mechanical strength. Recently, Matsubara et al., “Low-kFluorinated Amorphous Carbon Interlayer Technology for Quarter MicronDevices”, IEDM, p 369-372 (1996), have described the successfulintegration and use of α-FC as the intermetal dielectric in athree-level metallization structure. A 50% decrease in line capacitanceis reported using this dielectric material.

However, as geometries shrink, gap fill performance becomes asignificant issue. Gap fill performance generally refers to the abilityof a process to fill the area, known as trenches, between metal lines.Recently, the trend has been to incorporate high density plasmaprocesses into integrated sequences to take advantage of in situ sputteretch and deposition to achieve enhanced gap fill results. In HDP-CVD, abias power is coupled to the substrate to attract ions which sputter thefield of the substrate during deposition, thereby preventing a phenomenaknown as crowning where the deposition material converges over thetrench before the trench is completely filled with the depositionmaterial. By controlling the deposition rate on the field (i.e., thearea between the trenches) of the substrate, improved gap fillperformance in small features ≦0.25 μm can be achieved.

One problem associated with α-FC films is that application of a highbias power tends to enhance fragmentation of fluorine which is thenincorporated into the resulting film as loose unbonded F or CF_(x)(x=1-4). It has been well documented that organic fluorocarbon moleculeswill either form etching species such as F⁻ or polymerize under glowdischarge conditions. Whether etching or the polymerization reactionwill dominate depends on plasma energy, charged specie intensities,reactant ratios and surface temperatures. EP patent application Ser. No.5114253.8 discusses the problems associated with high bias power andattempts to resolve the problems by eliminating the use of high biaspower in the depositin of an α-FC film.

Another problem encountered is that fluorine generated during depositionof the fluorine containing dielectric materials is adsorbed by thechamber walls and chamber components and is out gassed during subsequentdeposition steps. The fluorine attacks the metal surfaces on thesubstrate and prevents good adhesion. Titanium, nitride is frequentlyused as a barrier layer between dielectric layers and metal layers andis somewhat resistant to diffusion of process gases. However, titaniumnitride does not substantially improve adhesion between the metalsurfaces and the fluorine containing dielectric materials.

Therefore, there is a need to improve the application of HDP-CVDtechnology for deposition of very low dielectric constant α-FC films. Itwould be advantageous to provide an α-FC film having a dielectricconstant (k) of 2.8 or less which can be deposited using high densityplasma deposition, exhibits good gap fill performance in features 0.25μm and smaller and which is stable with a single post deposition anneal.

SUMMARY OF THE INVENTION

The present invention provides a method of forming an amorphousfluorocarbon film having both thermal stability and a low dielectricconstant. The method comprises the steps of introducing a substrate intoa process chamber and positioning the substrate on a support memberconnected to a bias power source, introducing a carbon source gas and afluorine source gas into the process chamber, delivering a source powerto the chamber sufficient to strike a plasma in the chamber, andapplying a bias power to the support member at a power level sufficientto achieve in situ sputter deposition on the substrate. The carbon gassource and fluorine gas source are preferably introduced in sufficientamount to maintain an atomic ratio of F:C less than 2.

Another aspect of the invention provides a season coating of siliconnitride or silicon oxynitride on internal surfaces of the depositionchamber prior to substrate processing to prevent out gassing of fluorineor fluorine compounds from the chamber surfaces. In one embodiment,silicon nitride or silicon oxynitride is deposited on internal surfacesof a deposition chamber in an amount sufficient to block out gassing offluorine from the internal surfaces. The amount of outgassed fluorinecan be controlled to prevent unwanted incorporation of free fluorineinto the resulting fluorine containing film. This aspect of theinvention can be combined with the use of an adhesive layer formed onthe metal surfaces, such as the nitrogen treated Ti or TiN, to furtherprevent fluorine attack on the metal surfaces.

The present invention further provides a method of enhancing adhesion ofa fluorine containing dielectric material to metal surfaces formed on asubstrate, comprising the steps of depositing an adhesive metal layer,such as titanium (Ti) or titanium nitride (TiN) on a substratecomprising metal surfaces, forming a metal/N₂ surface on the adhesivemetal layer by exposing the adhesive metal layer to nitrogen, anddepositing a fluorine containing dielectric material on the metal/N₂surface of the adhesive metal layer. The deposited metal layer ispreferably exposed to a nitrogen plasma provided by capacitively orinductively coupling energy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is a simplified diagram of one embodiment of a high densityplasma chemical vapor deposition system according to the presentinvention;

FIG. 1b is a simplified cross section of a gas ring that may be used inconjunction with the exemplary CVD processing chamber of FIG. 1A;

FIG. 1c is a simplified diagram of a monitor and light pen that may beused in conjunction with the exemplary CVD processing chamber of FIG.1A;

FIG. 1d is a flow chart of an exemplary process control computer programproduct used to control the exemplary CVD processing chamber of FIG. 1A;

FIGS. 2a and 2 b illustrate a comparison of two micrographs having afilm deposited at high and low bias power, respectively;

FIG. 3 is a graph showing the relationship between bias power and filmshrinkage;

FIG. 4 is a graph showing the relationship between C₄F₈:CH₄ ratio andboth film shrinkage and deposition rate;

FIG. 5 is a graph showing the relationship between annealing time anddielectric constant;

FIG. 6a is a schematic partial sectional view of a substrate comprisingaluminum lines deposited by methods known in the art;

FIG. 6b is a schematic partial sectional view of the substrate of FIG. 4showing a titanium nitride layer deposited on the substrate and exposedto nitrogen according to the present invention; and

FIG. 6c is a schematic partial sectional view of the substrate of FIG. 5showing a fluorine containing dielectric material deposited on thesubstrate.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The present invention provides an improved method of depositing anamorphous fluorocarbon (α-FC) film on a substrate or other workpieceusing high density plasma chemical vapor deposition techniques.Generally, it has been discovered that the film quality and gap fillperformance can be enhanced by controlling the gas concentrations whileapplying a high bias power (˜100W or higher) to the substrate.Specifically, thermal stability and a low dielectric constant can beachieved in an α-FC film with good gap fill performance and improvedadhesion to metals by controlling the relative concentrations of afluorine source and a carbon source while applying a sputtering biaspower to the substrate. In one embodiment, an amorphous fluorocarbonfilm is deposited from methane (CH₄) and octafluorocyclobutane (C₄F₈)using a HDP-CVD reactor. The resulting film is thermally stable with adielectric constant (K) value<2.8 up to 450° C. The film is believed tohave an increased molecular weight, increased cross linking and improvedstress in comparison to known α-FC films.

The present invention also provides a method for depositing a seasoningfilm on the interior surfaces of the reactor to reduce the likelihood ofoutgassing of fluorine and other contaminants from the reactor walls andother components which further improves adhesion and stability of theresulting fluorine containing film. In one embodiment, a silicon nitrideor silicon oxynitride film is deposited at a thickness of about 100 Å onthe internal chamber surfaces.

The invention also provides a method for depositing an adhesion layer ona substrate, comprising the steps of depositing an adhesive metal layer,such as Ti or TiN, on a substrate, and exposing the adhesive metal layerto nitrogen. The substrate is preferably positioned adjacent a processzone in which a nitrogen plasma is generated to expose the depositedadhesive metal layer to nitrogen (“stuffed with”) to alter the structureof the deposited metal layer. This altered surface is believed toimprove the adhesion of the fluorine containing dielectric over theTi/TiN layer without such treatment.

The methods of the present invention are preferably performed on anUltima HDP-CVD™ Centura® System available from Applied Materials, Inc.located in Santa Clara, Calif.. The features of the system are generallydescribed below. It is to be understood that while the below describedHDP-CVD system is the best system known to the inventors, other systems,may also be used, or modified to be used, to advantage to accomplish themethods of the present invention.

FIG. 1A illustrates one embodiment of a HDP-CVD system 10 in which adielectric layer according to the present invention can be deposited.System 10 includes a chamber 13, a vacuum system 70, a source plasmasystem 80A, a bias plasma system 80B, a gas delivery system 33, and aremote plasma cleaning system 50.

The upper portion of chamber 13 includes a dome 14, which is made of adielectric material, such as alumina or aluminum nitride. Dome 14defines an upper boundary of a plasma processing region 16. Plasmaprocessing region 16 is bounded on the bottom by the upper surface ofsubstrate 17 and the substrate support member 18.

A heater plate 23 and a cold plate 24 surmount, and are thermallycoupled to, dome 14. Heater plate 23 and cold plate 24 allow control ofthe dome temperature to within about ±10° C. over a range of about 100°C. to 200° C.

The lower portion of chamber 13 includes a body member 22, which joinsthe chamber to the vacuum system 70 which has a throttle valve 26. Abase portion 21 of substrate support member 18 is mounted on, and formsa continuous inner surface with, body member 22. Substrates aretransferred into and out of chamber 13 at an upper loading position 57and moved to a lower processing position 56 in which the substrate isplaced on a substrate receiving portion 19 of substrate support member18. Substrate receiving portion 19 includes an electrostatic chuck 20that secures the substrate to substrate support member 18 duringsubstrate processing.

The source plasma system 80A includes a top coil 29 and side coil 30,mounted on dome 14. A symmetrical ground shield (not shown) reduceselectrical coupling between the coils. Top coil 29 is powered by topsource RF (SRF) generator 31A, while side coil 30 is powered by side SRFgenerator 31B, allowing independent power levels and frequencies ofoperation for each coil. This dual coil system allows control of theradiation density in chamber 13, thereby improving plasma uniformity.Side coil 30 and top coil 29 are typically inductively driven, whichdoes not require a complimentary electrode. In a specific embodiment,the top source RF generator 31A provides up to 2,500 watts of RF powerat nominally 2 MHz and the side source RF generator 31B provides up to5,000 watts of RF power at nominally 2 MHz. The operating frequencies ofthe top and side RF generators may be offset from the nominal operatingfrequency (e.g., to 1.7-1.9 MHz and 1.9-2.1 MHz, respectively) toimprove plasma-generation efficiency.

A bias plasma system 80B includes a bias RF (BRF) generator 31C and abias matching network 32C. The bias plasma system 80B capacitivelycouples substrate portion 17 to body member 22, which act ascomplimentary electrodes. The bias plasma system 80B serves to enhancethe transport of plasma species (i.e., ions) created by the sourceplasma system 80A to the surface of the substrate. In a specificembodiment, bias RF generator provides up to 5,000 watts of RF power at13.56 MHz.

Matching networks 32A and 32B match the output impedance of generators31A and 31B with their respective coils 29 and 30. The RF controlcircuit may tune both matching networks by changing the value ofcapacitors within the matching networks to match the generator to theload as the load changes. The RF control circuit may tune a matchingnetwork when the power reflected from the load back to the generatorexceeds a certain limit. One way to provide a co match, and effectivelydisable the RF control circuit from tuning the matching network, is toset the reflected power limit above any expected value of reflectedpower. This may help stabilize a plasma under some conditions by holdingthe matching network constant at its most recent condition.

A gas delivery system 33 provides gases from several sources to thechamber for processing the substrate via gas delivery lines 38 (onlysome of which are shown). Gases are introduced into chamber 13 through agas ring 37 and a top nozzle 45. FIG. 1B is a simplified, partialcross-sectional view of chamber 13 showing additional details of gasring 37.

In one embodiment, first and second gas sources, 34A and 34D, and firstand second gas flow controllers, 35A′ and 35D′, provide gas to a ringplenum 36 in gas ring 37 via gas delivery lines 38 (only some of whichare shown). Gas ring 37 has a plurality of source gas nozzles 39 (onlyone of which is shown in FIG. 1B) that provide a uniform flow of gasover the substrate. Nozzle length and nozzle angle may be changed toallow tailoring of the uniformity profile and gas utilization efficiencyfor a particular process within an individual chamber. In a preferredembodiment, gas ring 37 has 12 source gas nozzles.

Gas ring 37 also has a plurality of oxidizer gas nozzles 40 (only one ofwhich is shown), which in a preferred embodiment are co-planar with, andshorter than, source gas nozzles 39, and in one embodiment receive gasfrom a body plenum 41. In some embodiments it is desirable not to mixsource gases and oxidizer gases before injecting the gases into chamber13. In other embodiments, oxidizer gas and source gas may be mixed priorto injecting the gases into chamber 13 by providing apertures (notshown) between body plenum 41 and gas ring plenum 36. In one embodiment,third and fourth gas sources, 34B and 34C, and third and fourth gas flowcontrollers, 35B′ and 35C, provide gas to the body plenum via gasdelivery lines 38.

Referring again to FIG. 1A, chamber 13 also has top nozzle 45 and topvent 46. Top nozzle 45 and top vent 46 allow independent control of topand side flows of the gases, which improves film uniformity and allowsfine adjustment of the film's deposition. Top vent 46 is an annularopening around top nozzle 45. In one embodiment, first gas source 34A isa C₄F₈ or CH₄ source that supplies source gas nozzles 39 and top nozzle45. Source nozzle mass flow controller (MFC) 35A′ controls the amount ofC₄F₈ or CH₄ delivered to source gas nozzles 39 and top nozzle MFC 35Acontrols the amount of C₄F₈ or CH₄ delivered to top gas nozzle 45.Similarly, two MFCs 35B and 35B′ may be used to control the flow ofoxygen to both top vent 46 and oxidizer gas nozzles 40 from a singlesource of oxygen, such as source 34B. The gases supplied to top nozzle45 and top vent 46 may be kept separate prior to flowing the gases intochamber 13, or the gases may be mixed before they flow into chamber 13.Separate sources of the same gas may be used to supply various portionsof the chamber.

System controller 60 controls the operation of system 10. In a preferredembodiment, controller 60 includes a memory 62, such as a hard diskdrive, a floppy disk drive (not shown), and a card rack (not shown). Thecard rack may contain a single-board computer (SBC) (not shown), analogand digital input/output boards (not shown), interface boards (notshown), and stepper motor controller boards (not shown). The systemcontroller conforms to the Versa Modular European (VME) standard, whichdefines board, card cage, and connector dimensions and types. The VMEstandard also defines the bus structure having a 16-bit data bus and24-bit address bus. System controller 60 operates under the control of acomputer program stored on the hard disk drive or other computerprograms, such as programs stored on a floppy disk. The computer programdictates, for example, the timing, mixture of gases, RF power levels andother parameters of a particular process. System controller 60 includesa processor 61 coupled to a memory 62. Preferably, memory 62 may be ahard disk drive, but of course memory 62 may be other kinds of memory,such as ROM, PROM, and others.

System controller 60 operates under the control of a computer program.The computer program dictates the timing, temperatures, gas flows, RFpower levels and other parameters of a particular process. The interfacebetween a user and the system controller is via a CRT monitor 65 and alight pen 66, as depicted in FIG. 1C. In a preferred embodiment, twomonitors, 65 and 65A, are used, one mounted in the clean room wall forthe operators and the other behind the wall for the service technicians.Both monitors simultaneously display the same information, but only onelight pen (e.g., 66) is enabled. To select a particular screen orfunction, the operator touches an area of the display screen and pushesa button (not shown) on the pen. The touched area confirms beingselected by the light pen by changing its color or displaying a newmenu, for example.

The computer program code can be written in any conventional computerreadable programming language such as 68000 assembly language, C, C++,or Pascal. Suitable program code is entered into a single file, ormultiple files, using a conventional text editor, and stored or embodiedin a computer-usable medium, such as a memory system of the computer. Ifthe entered code text is in a high level language, the code is compiled,and the resultant compiler code is then linked with an object code ofprecompiled windows library routines. To execute the linked compiledobject code, the system user invokes the object code, causing thecomputer system to load the code in memory, from which the CPU reads andexecutes: the code to perform the tasks identified in the program.

FIG. 1D shows an illustrative block diagram of the hierarchical controlstructure of computer program 300. A user enters a process set numberand process chamber number into a process selector subroutine 310 inresponse to menus or screens displayed on the CRT monitor by using thelight pen interface. The process sets are predetermined sets of processparameters necessary to carry out specified processes, and areidentified by predefined set numbers. Process selector subroutine 310identifies (i) the desired process chamber in a multichamber system, and(ii) the desired set of process parameters needed to operate the processchamber for performing the desired process. The process parameters forperforming a specific process relate to process conditions such as, forexample, process gas composition and flow rates, temperature, pressure,plasma conditions such as RF power levels, and chamber dome temperature,and are provided to the user in the form of a recipe. The parametersspecified by the recipe are entered utilizing the light pen/CRT monitorinterface.

The signals for monitoring the process are provided by the analog inputand digital input boards of the system controller and the signals forcontrolling the process are output on the analog output and digitaloutput boards of system controller 60.

A process sequencer subroutine 320 comprises program code for acceptingthe identified process chamber and set of process parameters from theprocess selector subroutine 310, and for controlling operation of thevarious process chambers. Multiple users can enter process set numbersand process chamber numbers, or a user can enter multiple process setnumbers and process chamber numbers, so sequencer subroutine 320operates to schedule the selected processes in the desired sequence.Preferably, sequencer subroutine 320 includes a program code to performthe steps of (i) monitoring the operation of the process chambers todetermine if the chambers are being used, (ii) determining whatprocesses are being carried out in the chambers being used, and (iii)executing the desired process based on availability of a process chamberand type of process to be carried out, Conventional methods ofmonitoring the process chambers can be used, such as polling. Whenscheduling which process is to be executed, sequencer subroutine 320 canbe designed to take into consideration the present condition of theprocess chamber being used in comparison with the desired processconditions for a selected process, or the “age” of each particular userentered request, or any other relevant factor a system programmerdesires to include for determining scheduling priorities.

After sequencer subroutine 320 determines which process chamber andprocess set combination is going to be executed next, sequencersubroutine 320 causes execution of the process set by passing theparticular process set parameters to a chamber manager subroutine330A-C, which controls multiple processing tasks in chamber 13 andpossibly other chambers (not shown) according to the process setdetermined by sequencer subroutine 320.

Examples of chamber component subroutines are substrate positioningsubroutine 340, process gas control subroutine 350, pressure controlsubroutine 360, and plasma control subroutine 370. Those having ordinaryskill in the art will recognize that other chamber control subroutinescan be included depending on what processes are desired to be performedin chamber 13. In operation, chamber manager subroutine 330A selectivelyschedules or calls the process component subroutines in accordance withthe particular process set being executed. Scheduling by chamber managersubroutine 330A is performed in a manner similar to that used bysequencer subroutine 320 in scheduling which process chamber and processset to execute. Typically, chamber manager subroutine 330A includessteps of monitoring the various chamber components, determining whichcomponents need to be operated based on the process parameters for theprocess set to be executed, and causing execution of a chamber componentsubroutine responsive to the monitoring and determining steps.

Operation of particular chamber component subroutines, will now bedescribed with reference to FIG. 1D. Substrate positioning subroutine340 comprises program code for controlling chamber components that areused to load a substrate onto substrate support number 18. Substratepositioning subroutine 340 may also control transfer of a substrate intochamber 13 from, e.g., a PECVD reactor or other reactor in themultichamber system, after other processing has been completed.

Process gas control subroutine 350 has program code for controllingprocess gas composition and flow rates. Subroutine 350 controls theopen/close position of the safety shut-off valves, and also rampsup/down the mass flow controllers to obtain the desired gas flow rates.All chamber component subroutines, including process gas controlsubroutine 350, are invoked by chamber manager subroutine 330A.Subroutine 350 receives process parameters from chamber managersubroutine 330A related to the desired gas flow rates.

Typically, process gas control subroutine 350 operates by opening thegas supply lines, and repeatedly (i) reading the necessary mass flowcontrollers, (ii) comparing the readings to the desired flow ratesreceived from chamber manager subroutine 330A, and (iii) adjusting theflow rates of the gas supply lines as necessary. Furthermore, processgas control subroutine 350 may include steps for monitoring the gas flowrates for unsafe rates, and activating the safety shut-off valves whenan unsafe condition is detected.

In some processes, an inert gas, such as argon, is flowed into chamber13 to stabilize the pressure in the chamber before reactive processgases are introduced into the chamber. For these processes, the processgas control subroutine 350 is programmed to include steps for flowingthe inert gas into chamber 13 for an amount of time necessary tostabilize the pressure in the chamber. The above-described steps maythen be carried out.

Furthermore, the process gas control subroutine 350 includes steps forobtaining the necessary delivery gas flow rate for the desired processgas flow rate by accessing a stored table containing the necessaryvalues for a given process gas flow rate. Once the necessary values areobtained, the delivery gas flow rate is monitored, compared to thenecessary values and adjusted accordingly.

The process gas control subroutine 350 may also control the flow ofheat-transfer gas, such as helium (He), through the inner and outerpassages in the wafer chuck with an independent helium control (IHC)subroutine (not shown). The gas flow thermally couples the substrate tothe chuck. In a typical process, the wafer is heated by the plasma andthe chemical reactions that form the layer, and the He cools thesubstrate through the chuck, which may be water-cooled. This keeps thesubstrate below a temperature that may damage preexisting features onthe substrate.

Pressure control subroutine 360 includes program code for controllingthe pressure in chamber 13 by regulating the size of the opening ofthrottle valve in the exhaust portion of the chamber. There are at leasttwo basic methods of controlling the chamber with the throttle valve.The first method relies on characterizing the chamber pressure as itrelates to, among other things, the total process gas flow, size of theprocess chamber, and pumping capacity. The first method sets throttlevalve 26 to a fixed position. Setting throttle valve 26 to a fixedposition may eventually result in a steady-state pressure.

Alternatively, the chamber pressure may be measured, with a manometerfor example, and throttle valve 26 position may be adjusted according topressure control subroutine 360, assuming the control point is withinthe boundaries set by gas flows and exhaust capacity. The former methodmay result in quicker chamber pressure changes, as the measurements,comparisons, and calculations associated with the latter method are notinvoked. The former method may be desirable where precise control of thechamber pressure is not required, whereas the latter method may bedesirable where an accurate, repeatable, and stable pressure is desired,such as during the deposition of a layer.

When pressure control subroutine 360 is invoked, the desired, or target,pressure level is received as a parameter from chamber managersubroutine 330A. Pressure control subroutine 360 operates to measure thepressure in chamber 13 by reading one or more conventional pressuremanometers connected to the chamber, compare the measure value(s) to thetarget pressure, obtain proportional, integral, and differential (PID)values from a stored pressure table corresponding to the targetpressure, and adjust throttle valve 26 according to the PID valuesobtained from the pressure table. Alternatively, pressure controlsubroutine 360 may open or close throttle valve 26 to a particularopening size, to regulate the pressure in chamber 13 to a desiredpressure or pressure range.

Plasma control subroutine 370 comprises program code for controlling thefrequency and power output setting of RF generators 31A and 31B, and fortuning matching networks 32A and 32B. Plasma control subroutine 370,like the previously described chamber component subroutines, is invokedby chamber manager subroutine 330A.

The Deposition Process Sequence

At the 0.18 μm technology generation, it is expected that both damasceneand conventional dielectric gap fill fabrication schemes will be used.For application in conventional process flows, gap filling of 0.18 μmspaces with a 3:1 aspect ratio will be required. The inventors havediscovered a gap filling mechanism under HDP-CVD deposition conditionswhich demonstrates comparable performance with conventional oxides. Thepresent invention will now be described with reference to a preferredprocess sequence practiced on the above described processing system.

In one embodiment, the inventors have discovered that application of abias power>100W to the substrate support member and capacitively coupledto the substrate during deposition of an α-FC film results in improvedfilm composition and good gap fill performance in small features, i.e.,0.25 μm in width and smaller. The temperature of the substrate ispreferably maintained at a temperature below 450° C. during processing.It was believed prior to the present invention that increasing the biaspower above 100W resulted in more fragmentation of the fluorineprecursor which becomes a free F⁻ source which can be trapped in thefilm. Incorporation of excess F⁻ into the film decreases thecarbon-carbon crosslinking of the α-FC film and lowers the thermalstability of the film. In addition, free F⁻ has the deleterious effectsof causing current leakage and charge being trapped within the film. Inaddition, more free F⁻ in the reactant mixture increases the etch rateof the deposited film, thereby decreasing the deposition rate.

The present invention combats these problems by adding a carbon source,such as methane or acetylene, into the chamber to react with and bindthe fragmented fluorine. The carbon source also typically provides ahydrogen source to scavenge unwanted free fluorine atoms. It is believedthat increasing the available carbon in the reactant gases binds thefragmented fluorine and the hydrogen acts as a fluorine scavenger. Someof the C_(x)F_(y) fragments (x=1-4; y=3-8) are volatile and can bepumped away from the chamber. As a result, the resulting filmincorporates less free fluorine atoms and demonstrates improved chainbranching. Increased chain branching results in a more thermally stablefilm having a low dielectric constant.

Preferably, the carbon source is flown into the chamber to decrease theatomic ratio of F:C in the precursor gases to less than two (2). Bothflow rate and power levels are adjusted to ensure that the F:C ratio isless than two (2) in the chamber.

In one embodiment performed on a 200 mm substrate, the preferredprecursor gases are octafluorocyclobutane (C₄F₈) and methane (CH₄) whichare flown into the chamber at a selected rate to maintain the atomicratio of less than 2 (two), preferably in a range between about 20 sccmand about 200 sccm. Argon, or other inert gas, is flown into the chamberat a rate of from about 20 sccm to about 100 sccm to sputter the growingsurface in situ as deposition is performed on the substrate. A biaspower greater than 100W, preferably about 1000W, is applied to thesubstrate support member to achieve a preferred C—F bonding structure inthe film at an acceptable deposition rate. A bias power of about 1000Wprovided the desired gap fill performance at 0.25 μm widths. Othercarbon gas surfaces such as CH₄, C₂H₄, C₂H₆, C₂H₂, C₆H₆, CF₄, C₂F₆,C₃F₈, CHF₃, and C₆F₆ and fluorine gas sources such as CF₄, C₂F₆, C₃F₈,CHF₃ and C₆F₆ may be used so long as the atomic ratios of F:C availablein the chamber remain less than 2. Additionally, other inert bombardinggases known in the field can be used.

EXAMPLE 1

The experiment was conducted in an Ultima™ HDP-CVD reactor availablefrom Applied Materials, Inc. of Santa Clara, Calif. RF frequencies forsource and bias generators were 2.0 and 13.56 MHz. Maximum power outputof both generators was 5000W. An α-CF film was deposited by reaction ofoctafluorocyclobutane (C₄F₈) and methane (CH₄) under HDP-CVD plasmaconditions. The chamber pressure during deposition was less than 10mtorr. Both octafluorocyclobutane (C₄F₈) and methane (CH₄) were flowninto the chamber at a rate of about 50 sccm for gap fill deposition.Argon was flown into the chamber at a rate of about 50 sccm. A sourcepower of 1000W and a bias power of 1000W were applied to the source coiland the substrate support member, respectively. 7000 Å of an α-FC filmwas deposited on the substrate.

EXAMPLE 2 Comparative

In a comparative example, all parameters were the same except that thebias RF power delivered to the substrate support member was 100W.

FIGS. 2a and 2 b are SEMs which compare the results of the abovedescribed examples, respectively. The only difference between the twoprocesses was the level of bias power applied to the substrate and thesize of the feature being filled. FIG. 2a shows a 0.25 μm feature andFIG. 2b shows a 0.6 μm feature. The process using the higher bias powerof 1000W shows complete gap fill of the 0.25 μm feature. Both processesused a source RF power of 1000W. As shown in the micrographs, a voidexists in the gap between metal lines when the lower bias power was usedin the process. As the bias power is increased up to about 1000W, thegap fill performance improves so that smaller features are filledwithout the formation of voids.

FIG. 3 is a graph showing the relationship between thermal shrinkage andbias power. As the bias power is increased from about 100W to about1000W, thermal shrinkage in the resulting film is reduced from about 8%to less than about 1%. The thermal stability of an α-FC film wasmonitored by thickness change before and after annealing theas-deposited film at 400° C. in vacuum.

FIG. 4 is a graph showing the relationship between C₄F₈:CH₄ ratio andboth film shrinkage and deposition rate. It was discovered that filmshrinkage depends strongly on film composition and depositiontemperature. At 1000W, film shrinkage is at minimum when CH₄:C₄F₈=1(F:C≦2). Further increase in F content decreases the thermal stabilityof the α-FC film. Presumably, a film with higher F content is lesscross-linked and thus easy to deform at higher temperature. Low hydrogenand oxygen content in the film is another key to the thermal stabilitybecause the CH_(x) group is easy to dissociate at high temperature. TDSspectra confirms that CH and CF_(x) are the main desorption speciesduring anneal.

FIG. 5 is a graph showing the relationship between annealing time anddielectric constant. The dielectric constant of the α-FC film wascalculated from the capacitance measurement by a mercury probe at 1 MHz.The dielectric constant value after annealing at 400° C. in N₂ did notchange over time indicating thermal stability of the film.

Chamber Seasoning Step to Control Outgassing of Fluorine and OtherContaminants

It has also been discovered that out gassing of fluorine from theinternal surfaces of a deposition chamber can be blocked by seasoningthe chamber walls with a coating of silicon nitride, silicon oxynitride,FSG or combinations thereof The thickness of the coating on the chamberwalls is sufficient to block out gassing of fluorine from the internalsurfaces, preferably at least about 100 Å. The chamber seasoning processwill typically be carried out by CVD prior to positioning a substrate inthe deposition chamber. A process gas recipe is used to deposit siliconnitride or silicon oxynitride on internal surfaces of the chamber. Oneprocess for depositing the seasoning film reacts nitrogen with silane ata source power in the range of between about 1500-4500W. Nitrogen ispreferably delivered at a rate of about 100 to about 300 sccm and silaneis delivered at a rate of about 50 to about 120 sccm. The chambertemperature can be in the range of 60-70° C. or higher. Another suitabledeposition process is described in U.S. Pat. No. 5,589,233, whichdescription is incorporated by reference herein, wherein silicon nitrideor silicon oxynitride are deposited on a substrate and exposed internalsurfaces of a deposition chamber to block contamination by dopants whichare retained on the internal surfaces of the chamber. After seasoning ofthe chamber walls, a substrate having a patterned metal surface thereonis positioned in the chamber and processed according to the abovedescribed processes for depositing a fluorine containing layer or anyother known process for forming a fluorine containing film.

Improved Adhesion of Fluorine Containing Dielectric Layers to MetalSurfaces

In still another aspect of the invention, a method is provided fornitrogen stuffing of a metal layer for improving the adhesion of afluorine containing dielectric film to a substrate having exposed metalsurfaces such as patterned metal lines. In one aspect of the invention,a method is provided for nitrogen stuffing of deposited titanium ortitanium nitride to form a TiN/N₂ surface. Nitrogen ions in a plasmabombard the deposited metal layer and alter the structure of thedeposited metal film to improve adhesion of the dielectric film on themetal.

In one specific embodiment, the fluorine containing dielectric materialis an amorphous fluorocarbon material formed from deposition processgases including sources of carbon and fluorine, such as methane (CH₄)and octafluorocyclobutane (C₄F₈), respectively. Other carbon sources mayalso be used, however, methane or acetylene is preferred. Other fluorinesources include hexafluorobenzene (C₆F₆) and hexafluoropropane (C₃F₆).Additional fluorine ions may be generated to control fluorination of thepolymer film. The amorphous fluorocarbon is a chemically inert,amorphous dielectric material.

The N₂ stuffing of titanium nitride is carried out by first depositing atitanium nitride film, or other metal film, having a thickness of lessthan 500 Å. The titanium nitride is preferably deposited by sputtering atitanium target in a nitrogen (N₂) sputtering gas for between about 5and about 30 seconds. Then flow of N₂ is continued into the chamber, anda plasma is struck in the chamber to facilitate reaction between thedeposited TiN and the N₂ plasma. While a plasma is the preferred methodof stuffing, N₂ may be provided over the TiN and a different reaction,such as a thermal reaction, may facilitate the reaction between the TiNand the N₂. Where a plasma is used, N₂ is preferably provided into thechamber at a rate between about 5 sccm and about 500 sccm while thechamber is maintained at a pressure between about 0.5 mTorr and about 5Torr. Power is either capacitively or inductively coupled into thechamber to excite the N₂ into excited neutrals and the like which reactwith the TiN on the substrate. The substrate temperature is preferablymaintained in a range from about room temperature to about 500° C.

FIG. 6A shows a partial cross sectional view of a processed substrate400 having a dielectric layer 412, such as SiO₂, and patterned metallines 414 which are formed by conventional methods such as metallizationand plasma etching; Typical metals used to make vias or lines inprocessed substrates are aluminum or copper. The patterned metal linesare separated by trenches 416 which are to be filled with a lowdielectric material.

Referring to FIG. 6B, a TiN layer 418 is deposited on the substrate 400of FIG. 4A by physical vapor deposition (PVD) and then exposed tonitrogen to form a TiN/N₂ surface having a thickness greater than 5 Å.The TiN/N₂ surface is preferably continuous to protect the metal lines414 from attack by fluorine. The preferred TiN layer 418 comprisesanywhere from a monolayer up to about 200 Å of PVD TiN, following bynitrogen stuffing to form a continuous TiN/N₂ surface having a thicknessbetween 5 Å and 50 Å.

FIG. 6C is a schematic partial sectional view of the substrate 400 ofFIG. 4B showing an amorphous fluorocarbon layer 420 deposited on theTiN/N₂ layer 18. The amorphous fluorocarbon layer is a fluorinecontaining dielectric layer having a low dielectric constant asdescribed above.

While the foregoing is directed to the preferred embodiment of thepresent invention, other and further embodiments of the invention may bedevised without departing from the basic scope thereof, and the scopethereof is determined by the claims which follow.

What is claimed is:
 1. A method of adhering a fluorine containingdielectric material to metal surfaces on a substrate, comprising:depositing an adhesive metal layer on a substrate comprising metalsurfaces; exposing the adhesive metal layer to a nitrogen plasma; andthen depositing a fluorine containing dielectric material on theadhesive metal layer.
 2. The method of claim 1, wherein the adhesivemetal layer is a Ti or TiN layer.
 3. The method of claim 1, wherein themetal surfaces on the substrate comprise aluminum lines.
 4. The methodof claim 1, wherein the adhesive metal layer is deposited by physicalvapor deposition.
 5. The method of claim 1, wherein the fluorinecontaining dielectric material is an amorphous fluorocarbon material. 6.The method of claim 1, wherein the adhesion metal layer has a surfacecomprising nitrogen after the exposing to a nitrogen plasma and thesurface has a thickness greater than 5 Å.
 7. The method of claim 1,wherein nitrogen is provided at a rate between about 5 sccm and about500 sccm to form the plasma.
 8. A method for depositing an adhesionlayer on a substrate, comprising: depositing a titanium nitride layer onpatterned metal lines an the substrate; exposing the titanium nitridelayer to a nitrogen plasma; and then depositing a fluorine containingdielectric material on the titanium nitride layer.
 9. The method ofclaim 8, wherein the metal lines are aluminum lines.
 10. The method ofclaim 8, wherein the titanium nitride layer is deposited by physicalvapor deposition.
 11. The method of claim 8, wherein the fluorinecontaining dielectric material is an amorphous fluorocarbon material.12. The method of claim 8, wherein the titanium nitride layer has asurface comprising nitrogen after the exposing to a nitrogen plasma andthe surface has a thickness greater than 5 Å.
 13. The method of claim 8,wherein nitrogen is provided at a rate between about 5 sccm and about500 sccm to form the plasma.
 14. A method of processing a substratehaving exposed metal lines, comprising: depositing a TiN layer on thesubstrate by physical vapor deposition; providing nitrogen to a processzone adjacent the substrate at a pressure between about 0.5 mTorr andabout 5 Torr; striking a plasma in the process zone; exposing the TiNlayer to the plasma; and then depositing a fluorine containingdielectric layer on the TiN layer.
 15. The method of claim 14, whereinthe nitrogen is provided into the process zone at a rate between about 5sccm and about 500 sccm.
 16. The method of claim 14, wherein the exposedmetal lines on the substrate comprise aluminum lines.
 17. The method ofclaim 14, wherein the fluorine containing dielectric material is anamorphous fluorocarbon material.
 18. The method of claim 14, wherein theTiN layer has a surface comprising nitrogen after the exposing to plasmaand the surface has a thickness greater than 5 Å.